1. Field of the Invention
The present invention relates to a computer implemented, post production, lumped element or microstrip tuning method which relies on actual measurements of circuit parameters and on a priori knowledge of a specific circuit's desired response characteristics.
2. Description of the Prior Art
The tuning of an electrical circuit in the post production stage currently requires extensive human interface and intervention. A highly trained, skilled technician must individually test and tune each element of the circuit under test to achieve an ideal or specified circuit performance.
This manual post production tuning process is expensive because of the man-hour intensive, concentrated efforts required to reach circuit optimization. A skilled technician testing either lumped circuit elements such as resistors and capacitors or microwave, microstrip hybrid micro-electronic devices utilizes the same test and tune iterations striving towards ideal circuit performance.
First, the technician must test the circuit to be tuned in order to ascertain the circuit's existing level of performance. Next he must produce some physical change in the circuit elements, called a perturbation, one at a time. This individual element change will result in overall system performance change which is registered the second time the overall circuit performance is checked. Obviously, this time consuming circuit optimization process when performed for a circuit having a multiplicity of elements requires many man-hours of testing and tuning. Further, these time consuming circuit element adjustments require skilled technicians painstakingly probing the circuit under test and empirically determining the optimum element combinations necessary to cancel the myriad of effects of individual manufacturing and component tolerances.
The problem to be solved then is the development of a post production testing and tuning method which requires minimum human intervention and which can be fully automated. This method must be operable with lumped element circuits as well as microwave microstrip circuits. Specifically, this method will utilize the physical perturbation of individual circuit elements in concert with a mathematical optimization algorithm to achieve overall optimum circuit response.
Microwave amplifier modules usually require post production tuning to meet all technical specifications. These time consuming circuit adjustments are now presently performed by skilled technicians who again must painstakingly probe the circuit and empirically determine the optimum tuning combinations.
Computer-aided design and manufacturing of microwave modules has resulted in more uniform circuits by careful design analysis and control of these critical tolerances. However, these aids in design and manufacture do not totally preclude the necessity of post production tuning.
In order to reduce the skill requirements of the operators involved in the post production tuning process of microwave amplifiers, and thereby also reduce production costs a need has developed to apply computer based techniques to post production tuning of microwave amplifiers.
The automated post production tuning problem has been traditionally approached as a mathematical optimization problem. A computer model of the circuit to be tuned is created and the actual circuit parameters are then measured. The ideal computer generated response of the circuit is then related to the actual circuit response and a tuning algorithm is developed. This algorithm is a linear approximation of the circuit performance function. It updates the actual network tuning element configurations based on gradient data obtained by computer simulation of the network performance response to small changes in the tuning element values.
The traditional technique presupposes that a comprehensive computer model of the circuit can be realized. When one cannot rigorously define a transfer function for the network, it is not possible to construct such a computer model, and consequently the technique cannot be used. Such is the case for amplifiers which operate in saturation. Moreover, for all but the most simple microwave circuits, which have minimal tuning time requirements, it is not practical to construct an exhaustive computer model and an effective approximation algorithm which can provide enough information to tune an actual circuit.
The problem to be solved then for the post production tuning of microwave amplifiers is the development of a post production tuning technique which is hardware oriented and does not rely solely on information from a computer model of the circuit to be tuned. It would be an advantage for the computer model to be independent of the network transfer function, and based upon measurements of the actual circuit performance parameters. Knowledge of actual circuit performance parameters would utilize the circuit designer's knowledge of the basic circuit response characteristics to best advantage. It would further be an advantage to develop a post production tuning technique wherein the gradient algorithm used is not a purely mathematical construct, but a flexible formula which receives hardware dependent inputs specified by the circuit designer.
Finally, a fully automated, computer controlled, post production tuning station would most fully realize a significant cost reduction in post production processing. The elimination of the hands-on human interface by highly skilled technicians would decrease post production tuning time and therefore costs.